This invention relates to a cylinder lock with pairs of half tumblers inserted into the tumbler inserting holes formed in the key rotor.
The so-called "picking" of a cylinder lock, i.e., a cylinder lock being unlocked dishonestly without its key, may be effectively prevented by increasing the number of tumblers which are slidably engaged with the locking engagement grooves of the cylinder body. However, since it is impossible to reduce the pitch of arrangement of the tumblers in the key rotor to an extremely small value; that is, the pitch of arrangement of the tumblers in the key rotor is limited, the number of tumblers is determined from the length of the key rotor or key. In order to overcome this limitation, a method has been disclosed in which two half tumblers are inserted in one tumbler inserting hole, so that the number of tumblers is increased with the length of the key rotor or key maintained unchanged.
It is true that the number of tumblers can be increased by inserting two half tumblers in each tumbler inserting hole. However, the conventional cylinder lock of this type has a minimum fear that the lock may be picked when, with the key rotor turned slightly by picking one of the half tumblers, the other half tumbler is picked. Although it is impossible to practically pick the conventional cylinder lock of this type by the manner noted above because the picking will take much time and labor, it is required to provide a cylinder lock which is more positively protected from picking.